In a conventional laser printer, power is supplied from a commercial power supply and the supplied power is applied to a power supply circuit built in the printer. From the power applied thereto, the power supply circuit generates DC voltages necessary for the laser printer, such as 3.3 V used as a low voltage for control circuits and the like, and 24 V used in motors, other drive systems and high-voltage circuits, etc. Commercial power differs in voltage and frequency depending upon the country or area.
Safety standards for the control devices of image printers such as laser printers have been defined in various countries. For example, according to the IEC-1000-3-3 standard in Europe, limit values on voltage fluctuation and flicker have been defined. Furthermore, according to the specifications of IEC-1000-3-3, the rated supply voltage and frequency of commercial power are 220 to 250 V and 50 Hz, respectively.
Ordinarily, in control of a fixing heater in a laser printer, the resistance value of a ceramic heater is optimized so as to satisfy the specifications and obtain appropriate electrophotographic fixation. In terms of controlling the temperature of the fixing heater, on/off duty and frequency are regulated to perform control so as to optimize voltage fluctuation and flicker value.
In North America, on the other hand, the rated voltage and frequency of commercial power are 120 V and 60 Hz, respectively. Consequently, it is necessary to control the resistance value and fixing temperature of the ceramic heater optimum for the commercial power supply.
In the prior art, therefore, the power supply circuit and fixing heater unit are each constructed differently depending upon the supply voltage of each country or area. In addition, the control board of the printer also performs heater control that differs depending upon the supply voltage, and therefore the control board is constructed differently according to the country or area. If printer control boards are thus prepared in accordance with the commercial power supply of each country or area, this will lead to an increase in types of printer control boards and have an adverse effect upon productivity.